Analysis of Feed Defocus's Effects on a Ka-Band Parabolic Antenna

摘要

The parabolic reflectors of deep space antennas are influenced by many facts, such as fabrication error, gravity and thermal deformation, which induce the feed deviating from the focal point of the paraboloid. The feed defocus would introduce phase errors over the paraboloidal dish, and degrade the antenna performance. In this paper, first the feed defocus is discussed from the view of reflector geometry, and the corresponding path length difference is derived. Then the effects on a Ka-band deep space parabolic antenna with 35-m diameter are analyzed as an example. From geometrical analysis and numerical calculations, the effects of feed defocus on some important antenna parameters such as gain, sidelobe level and pointing error are given and summarized. Finally, a method of feed defocus calibration is proposed.